1. The Field of the Invention
The present invention relates to highly dispersed nanoparticle catalysts. In particular, embodiments of the present invention relate to dispersed nanoparticle catalysts that are combined with tobacco to reduce unwanted combustion and pyrolysis products such as carbon monoxide.
2. Related Technology
Burning tobacco can generate potentially undesirable small molecules such as carbon monoxide and nitric oxide. During smoking, these molecules are formed in three ways: (1) thermal decomposition (i.e., pyrolysis), (2) incomplete combustion, and (3) reduction of carbon dioxide with carbonized tobacco.
During smoking a typical cigarette has three distinct regions as it is consumed: the combustion zone, the pyrolysis/distillation zone, and the condensation/filtration zone. The “combustion zone” is the burning zone of the smoking article. Temperatures in the combustion zone range from about 700° C. to about 950° C. The rate of heating can go as high as 500° C./second depending on the rate of inhalation or puffing. The concentration of oxygen in the combustion zone is low since oxygen is being consumed to combust the tobacco to produce carbon dioxide, water vapor, and various organics. The low oxygen levels can increase the formation of undesirable small molecules such as carbon monoxide and/or nitric oxide.
The combustion reaction is highly exothermic and the heat generated is carried by gas to the pyrolysis/distillation zone. The low oxygen concentration coupled with the high temperature can lead to the reduction of carbon dioxide to carbon monoxide by carbonized tobacco in the “pyrolysis zone”, which is the region behind the combustion zone. Temperatures in this region can range from about 200° C. to about 600° C. The pyrolysis zone is where most of the carbon monoxide is produced. The major reaction in this region is the pyrolysis (i.e., thermal degradation) of the tobacco that produces carbon monoxide, carbon dioxide, smoke components, and charcoal from the heat generated in the combustion zone.
The third region of a typical cigarette is the condensation/filtration zone. Temperatures in this zone range from ambient to about 150° C.
Recently, catalysts have been developed to remove undesired chemicals in tobacco smoke. The catalyst is applied to the tobacco, cigarette filter, or other component of the smoking apparatus to oxidize carbon monoxide and light organic compounds to form harmless compounds such as carbon dioxide. Various catalysts have been developed in an attempt to eliminate undesired combustion and pyrolysis products from tobacco smoke. Existing catalysts have used a wide variety of catalyst components. For example, existing tobacco catalysts use a ceramic material such as alumina or zirconia which is combined with a platinum group metal. Other existing catalyst are made from metal oxides, such as vanadium pentoxide, mixtures of iron and manganese, or iron by itself.
Existing catalysts, however, are inefficient, cost prohibitive and/or nonselective in destroying undesirable combustion and pyrolysis products. One particularly difficult problem is the destruction of the catalyst particles by the heat generated in combustion and/or pyrolysis. While the high temperatures can be useful or even necessary for catalyst function, the extreme temperatures can cause deactivation of the catalyst, such as by sintering or agglomeration. Agglomeration of catalyst particles dramatically reduces the catalytic surface area, thus reducing the efficiency of the catalyst. Because of the reduced efficiency of existing catalysts, the tobacco must have higher loadings of catalyst to achieve the desired destruction of carbon monoxide and light organics. In the case of existing iron catalysts, the required catalyst loading is too high to be practical.
Therefore, what is needed is a cost effective catalyst that can be combined with tobacco in reasonable amounts to eliminate undesired combustion and pyrolysis products.